1. Field of the Invention
The present invention relates to a controller of an injection molding machine that controls each operation process in a molding cycle by variably controlling a rotation speed of a driving motor in a hydraulic pump.
2. Description of the Relevant Art
As an injection molding machine on which a controller for controlling each operation process in a molding cycle by variably controlling a rotation speed of a driving motor in a hydraulic pump is mounted, an injection molding machine disclosed in Japanese Patent Laid-Open No. 2007-69500 is known.
This injection molding machine uses a variable discharge type hydraulic pump that can set a fixed discharge flow rate by changing a swash plate angle and is provided with controlling means for controlling each operation process by switching the hydraulic pump to the fixed discharge flow rate corresponding to each operation process set on the basis of a predetermined condition and by variably controlling a rotation speed of a servo motor connected to a servo circuit, with which energy saving performance can be improved, a running cost can be reduced, and an entire initial cost can be reduced. Moreover, moldability and molding quality can be improved, reliability can be enhanced and it can have a longer operating life.
However, the above-mentioned conventional injection molding machine (controller) has the following problems to be solved.
First, since each operation control is made by variably controlling the rotation speed of the servo motor driving the hydraulic pump, a pressure detected value used for feedback control of pressure is obtained from a pressure sensor for detecting a hydraulic pressure discharged from the hydraulic pump and a speed detected value used for feedback control of speed is obtained from an encoder for detecting the rotation speed of the servo motor. By configuring such control system, a physical amount close to the servo motor can be detected and instability in control involved with response delay and the like can be avoided, but since the detection is carried out at a place far from an actual control target, pressure loss based on viscosity by a pressure oil caused by disturbance (temperature change and the like) and its fluctuation generated in a hydraulic circuit in the middle can not be ignored, and particularly, an adverse effect on a molding quality such as a reduction tendency and large variation of a molded product weight is not ignorable.
Secondly, since the pressure detected value and speed detected value are detected at the place far from the actual control target, the obtained pressure detected value and speed detected value are so-called deemed values including temporal lag or error with respect to the pressure and speed generated at the actual control target. Therefore, in order to ensure accurateness (accuracy), adjustment or setting of the control system considering such temporal lag or error is needed, and the adjustment work or setting work becomes cumbersome.